Polyolefin resin films are broadly used for the purposes such as surface protection, impartation of water resistance and oil resistance, and enhancement of surface gloss on packaging bags and printing papers. In particular, it is broadly practiced that a film is subjected to thermocompression bonding to the surface of a printed paper to achieve surface protection. As films to be used for such a purpose, are frequently used laminated films comprising a low-melting ethylene based resin laminated on a biaxially stretched polypropylene film substrate having excellent optical characteristics in gloss and transparency.
As such laminated films, there are proposed laminated films prepared by laminating a resin composition comprising a mixture of an ethylene/alkyl ester copolymer and an ethylene/vinyl acetate copolymer on a biaxially stretched polypropylene film substrate by the melt extrusion lamination method (JP-A-56-42652, JP-B-4-2431, and JP-A-3-73341) and a process of producing print laminate articles by laminating a resin adhesive layer in which an ethylene based resin is compounded in a linear ethylene/α-olefin copolymer prepared by using a metallocene compound as a catalyst only by thermocompression bonding (JP-A-7-117197).
In the case of laminating an ethylene based resin on a biaxially stretched polypropylene film substrate, for attaining interlaminar adhesion at levels at which no practical problem occurs, it was necessary to oxidize the film substrate and laminate the ethylene based resin via an anchor coating agent.
However, the method of using an anchor coating agent involved problems such that a drying step of the solvent is necessary so that the equipment becomes large-scaled; the working environment becomes worse with diffusion of a solvent odor emitted during the drying; that a danger of occurrence of fire is high; and that a processing rate cannot be increased due to limits of a coating or drying ability.
Further, at present, in films prepared by laminating a resin adhesive layer on a biaxially stretched polypropylene based film substrate without using an anchor coating agent, an interlaminar adhesive force between the film substrate and the resin adhesive layer is weak, and after thermocompression bonding to a printing paper, bubbles remain between the printing paper and the film to form portions having low transparency, whereby visibility of printing information is impaired to deteriorate an appearance (collapse). Moreover, since peeling easily occurs between the stretched polypropylene based film and the resin adhesive layer, a laminate adhesive strength is weak, leading to a problem such that the resulting articles cannot be used as a commercial product.
The invention is to provide a laminated film of a propylene resin layer and an ethylene resin layer, which does not require solvent removal and recovery devices, etc., is low in influences against working environments and a danger of occurrence of fire, and has a high interlaminar adhesive force without using an anchor coating agent.